Air traffic managers in the National Airspace System (NAS) regularly implement various traffic management initiatives to handle traffic in a safe and efficient manner. One such initiative is the Miles-in-Trail (hereafter MIT) restriction, which is used when downstream traffic congestion at airports or in sectors is anticipated. Imposed MIT is the value of spacing required between aircraft flying along a certain path. They help the air traffic managers control the flow of aircraft downstream of an air traffic control facility. MITs may be implemented independently or in conjunction with other initiatives (e.g., a severe weather avoidance plan route or a playbook route, ground delay programs, etc.).
A typical scenario is shown in FIG. 1. Here, there are three Air Route Traffic Control Centers (ARTCC) identified as ZLC (Salt Lake City Center), ZMP (Minneapolis Center), and ZDV (Denver Center). The primary metering constraint of concern here is ABR (Aberdeen, S. Dak.). The dashed lines represent air traffic flow streams. The passback boundary locations are identified as B1-B4. The problem arises when, for example in ZMP, where there are two converging streams that join at ABR (Aberdeen, S. Dak.). When congestion is anticipated to occur downstream of ABR and a primary MIT constraint is imposed at a ABR, a MIT value must be “passed back” to HLN (Helena, Mont.) and RAP (Rapid City, S. Dak.) such that aircraft are delayed at B1 and B2 to ensure that the required MIT value is achieved at ABR. Since traffic from CZI (Crazy Woman, Wyo.) and EKR (Meeker, Colo.) travels to RAP, MIT constraints need to be passed back at B3 and B4 as well.
Traffic in both streams (from HLN and RAP) must be considered in determining the passback values so that the merged stream that exits B1 and B2 and meets at ABR satisfies the primary metering constraint at ABR. Thus, in order to ensure that traffic exiting ABR meets the primary metering constraint, passback values must propagate back to B1, B3 and B4 (for the southern stream) and through B2 (for the northern stream). Also consider that independent aircraft (shown in FIG. 1 as X1) that may not pass through a boundary at all may also join mid-stream further exacerbating the problem.
Previous methods for MIT calculation make gross assumptions about required spacing when congestion occurs and therefore are inherently suboptimal. If the MIT required value at ABR must be 15 nmi, the general assumption is that the input stream from B1 (through RAP) must be 30 nmi and the input stream from B2 (through HLN) must be 30 nmi such that when they merge, 15 nmi can be achieved at ABR. The previous solution did not consider the density of traffic on the RAP stream as compared to the HLN stream (or vice versa).
In light of the shortcomings of the previous solution, there exists a need for a system and method for managing air traffic that optimizes MIT throughout the system thus improving the efficiency of traffic flow (by minimizing delays) through the entire National Airspace system.